1. Field of the Invention
The invention concerns a saddle-coil arrangement for a cathode ray tube, i.e. a saddle-coil arrangement with a funnel-shaped coil carrier made of insulating material which carries two saddle-coil windings. The coil carrier usually consists of two coil-carrier halves. More exactly, the invention concerns coil-carrier halves of this sort and also a saddle-coil arrangement which features two coil-carrier halves, each having a winding. These saddle-coil arrangements are used for the horizontal deflection of the electron beams in a cathode ray tube. In the following, it is assumed that the cathode ray tube is one having several separately controllable electron beams, e.g. a colour picture tube. However, the invention can also be applied to monochrome tubes.
2. Description of the Prior Art
Saddle-coil arrangements with a coil carrier and two single windings are manufactured in two fundamentally different ways. In one process, the single windings are wound around a special shape, then baked and finally attached to the support. In the other process, which is solely concerned here, each single winding is wound directly onto a coil-carrier half and the two wound coil-carrier halves are assembled to form the saddle-coil arrangement. Coil-carrier halves for arrangements thus built feature the following guide parts for the winding:
a front groove at the front, wider diameter of the funnel-shaped carrier half, PA1 a rear groove at the rear, narrower diameter of the carrier half, PA1 several left slots which connect the two grooves near their left ends, and PA1 several right slots which connect the two grooves near their right ends and which lie in angular symmetry with the left slots.
When inserting the winding wires into the slots, winding starts, for example, at the rear groove and then the wire passes into the first right slot (viewed from the front for the lower carrier half) until it reaches the front groove. In the front groove it passes from the right to the left until the first left slot is reached. In this slot it then passes to the rear and there it passes from the left to the right in the rear groove. In most cases, several wires are introduced at the same time, e.g. four wires, each with a diameter of 0.375 mm. When the required total number of windings, e.g. 10 windings, each consisting of four wires, are inserted into the first slots, the second slots are supplied with windings, etc. In saddle coils used for the above-mentioned purpose, there are normally 4-6 slots on each side of a coil-carrier half.
As a result of the winding technique used and for reasons of space, the winding is manufactured by routing the wire at different points and drawing it at different forces. When the wire is passed from a slot to a groove the wire can be easily maintained on the bottom surface of the slot; however, when the wire is passed from a groove to a slot the winding technique causes the wire to lie on previously-wound wire, thereby effectively making the slot longer at a groove-to-slot junction, producing asymmetrical windings which lead to image defects. These image defects are represented in an exaggerated form in FIG. 5a. In FIG. 5a it is assumed that three horizontal white lines should be presented on a screen 10, i.e. one in the centre and one at both the bottom and top of the screen. Each white line is composed of a red line r, a green line g and a blue line b. Ideally, these lines should be superimposed across the total width of the screen. However, with previous conventional saddle-coil arrangements, i.e. arrangements with windings wound directly onto a coil carrier, the systematic image defects according to FIG. 5a occur. The three coloured single lines at the top and bottom of the screen each spread outwards at increasing and unequal distances from the horizontal to one side of the screen. The central white line is split into its three composite colour single lines at its ends near the edges of the screen (twist).
Efforts have been made to reduce the systematic defects illustrated by means of FIG. 5a as much as possible by assuring that the winding forces exerted when the windings are manufactured are as constant as possible. However, residual defects proved to be unavoidable.
The problem of reducing the described image defects still further has therefore existed for many years.